Waves

• Secondary (s-waves) are transverse waves that travel through the Earth from an earthquake
• Primary (p-waves) are longitudinal waves that travel through the Earth from an earthquake
• Progressive waves are waves where the peaks and troughs, or compressions and refractions, move through the medium as energy is transferred.
• Longitudinal waves are waves that oscillate parallel to the direction of energy transfer.
• Transverse waves are waves that oscillate perpendicular to the direction of energy transfer.
• Peaks are the maximum positive amplitude of transverse waves
• Troughs are the maximum negative amplitudes of a transverse wave
• Frequency = 1 / time period measured in Hz
• Wave speed = wave length x frequency measured in m/s
• Electromagnetic spectrum

  • radio waves
  • microwaves
  • infrared
  • visible light
  • ultra violet
  • x-rays
  • gamma rays
• Speed of light = 3.0 x 10^8 m/s
• The frequency is the number of oscillations in one second
• Waves transfer energy without transferring matter. You can also use waves to transfer information eg radio waves
• Transverse waves eg any electromagnetic wave travel through a vacuum whereas longitudinal waves eg sound waves have to travel through a medium
• Earthquake waves

  • primary waves - cause the initial tremors and are longitudinal waves thaat push or pull on material
  • secondary waves - slower waves that causetremors a few minutes later and are transverse waves which shake material side to side (cannot travel through liquid)
  • L waves - they are the slowest wave
• Humans have a hearing in the range of roughly 20Hz - 20000Hz anything higher than this is known as ultrasound
• Refraction of waves is the change of the direction in which they are travelling when they cross a boundary between one medium and another. This due to the change in speed of the wave in different mediums
• Compressions are moving regions in which the medium is denser or has a higher pressure than the surrounding medium
• Rarefactions are moving regions in which the medium is less dense or has less pressure then the surrounding medium
• Equilibrium position is the resting position of waves or particles in an oscillation
• Resorting force is a force that tries to return a system to its equilibrium position
• The direction of a particle in a wave is shown by the rule that the particle is going towards the postion of the particles behind it
• Phase difference = distance between particle (x) / wave length (λ) x 360
• Wavelength is the minimum distance between two point in phase on adjacent waves
• Displacement is the distance from the equalibrium position in a particluar direction
• Amplitude is the maximum displacement from the equalibrium position of a wave.
• Reflection vs Refraction

  • frequency doesn’t change in both
  • both happen with all waves
  • refraction in waves changes from one medium to another whereas reflection is in one medium
• wave speed is directly proportional to the wave length eg is wave speed decreases so does the wave length
• all angles are measured from the normal
• ray bends towards the normal then the wave is slowing down

  ray bends away from the normal then the wave has sped up
• refractive index of a material (n) = speed of light in a vacuum (C) / speed of light through the material (V)
• The angle at which the light is bent depends in the relative speeds of light through the two materials

  The greater the refractive index the move the light entering the material is refracted towards the normal
• Refractive law :

  • $n sin \theta =$$k$
  • $n1 sin \theta1 =$$n2 sin \theta 2$